Sorry that this may be a little off topic for a frequent flyer board but I figured the members here would be the best source of good information.

My wife and I are flying into Dublin in August and will end up in Killarney. We want to take the train to Belfast on a Sunday morning. We tried to book first class from Mallow through Dublin and on to Belfast but the Irish Rail website will only allow standard class which we booked.

Any suggestions on how to upgrade to first class.

Much thanks in advance